This invention relates to a novel focus-mask-type CRT (cathode-ray tube). The CRT comprises a color-selection structure which, when operating voltages are applied thereto, produces a plurality of substantially rectangular quadrupolar-focusing lenses therein and may also produce a related array of dipolar-deflection lenses therein. In this document, as in the prior art, "square" is included within the meaning of "rectangular."
CRTs with quadrupolar-focusing color-selection structures have been described previously as embodied in a two-layer structure in U.S. Pat. No. 4,059,781 issued Nov. 22, 1977 to W. M. van Alphen et al. and as a three-layer structure in U.S. patent application Ser. No. 161,603 filed June 20, 1980 by C. A. Catanese et al. The color-selection structures of these prior CRTs each comprise at least one set of parallel conductors held in position to another array of parallel conductors or to an apertured masking plate by solid insulators. CRTs with dipolar-deflecting-and-quadrupolar-focusing lenses have been described previously as embodied in a two-layer structure in U.S. Pat. No. 4,207,490 issued June 10, 1980 to R. F. Van der Ven and U.S. Pat. No. 4,316,126 issued Feb. 16, 1982 to E. F. Hockings et al. and in a three-layer structure in U.S. Pat. No. 4,311,944 issued Jan. 19, 1982 to S. Bloom et al. The color-selection structures of these prior CRTs each comprise at least one set of parallel conductors held in position with respect to an apertured masking plate by solid insulators.
In all of the prior quadrupolar-focusing color-selection structures, the parallel conductors are individual pieces, such as metal strips or metal wires, that are separately attached to the structure with solid insulators. This separateness presents a major fabrication problem of precisely positioning and attaching the many individual pieces, and major operational problem of maintaining the relative positions of these many pieces with respect to the other parts of the structure.
The prior structures produce substantially rectangular quadrupolar lenses in rectangular openings in the color-selection structure. Where an apertured masking plate comprises the structure, the rectangular apertures therein have been produced by etching a metal layer. Such etching process produces apertures with rounded corners, which are less desirable than the desired unrounded corners.